In conventional wireless communications systems, mobile devices or other user equipment transmit information to a network, and receive information from a network, such as via a base station. In some networks, the base stations or other network entities which transmit information to the user equipment may include different antenna configurations, such as different numbers of antennas, e.g., one antenna, two antennas or four antennas, and/or may transmit the information in accordance with different transmission diversity schemes. In this regard, a base station with a single antenna may transmit information without any transmission diversity scheme, while base stations with two or four antennas may transmit information in accordance with a transmission diversity scheme or a specific transmission diversity scheme out of a set of different available transmission diversity schemes. As used herein, the information regarding the antenna configuration, e.g., the number of antennas, and/or the transmission diversity scheme shall be commonly referenced (both individually and collectively) as antenna configuration information. In order to effectively receive information from a base station, for example, the user equipment must have know or recognize the antenna configuration and/or the transmission diversity scheme utilized by the base station. A mobile device is able to properly demodulate a received signal only after correctly determining the antenna configuration, i.e., the number of transmit antennas and/or the transmission diversity scheme of a base station. Since the antenna configuration information is needed in order to properly demodulate the received signal, the antenna configuration information must be determined by the user equipment with very high reliability.
For example, in an Evolved Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access Network (E-UTRAN), the user equipment can gather antenna configuration information regarding the base station, termed an eNodeB in E-UTRAN, using data contained within orthogonal frequency division multiplexing (OFDM) symbols of a message. By way of example, the technical specifications of the Third Generation Partnership Project (3GPP) and, in particular, 3GPP TS 36.211, REL 8 and 3GPP TS 36.212, REL 8 allows for an approach for providing antenna configuration information. In this regard, the user equipment can extract antenna configuration information from provided reference signals or by attempts to decode data within a physical broadcast channel (PBCH).
FIGS. 1a-1f depict sub-frames within a conventional cyclical prefix for various antenna configurations and transmission diversity schemes in an E-UTRAN system. The sub-frames of FIGS. 1a-1f include six physical resource blocks (PRBs), i.e. 1080 kHz (72 sub-carriers), each of which comprises a sub-frame #0. Each sub-frame can consist of a plurality of resource elements which fill two slots, namely, a slot #0 and a slot #1. Each slot can, in turn, be comprised of a series of orthogonal frequency division multiplexing (OFDM) symbols which represent respective channels of information. In this regard, the sub-frames of FIGS. 1a-1f can include a physical downlink (or download) control channel (PDCCH), a physical downlink shared channel (PDSCH), a primary synchronization channel (P-SCH), a secondary synchronization channel (S-SCH), a physical broadcast channel (PBCH), and unused sub-carriers.
The E-UTRAN sub-frame #0 also includes a plurality of reference signals which fill predetermined resource elements which depend upon the antenna configuration. For example, in the sub-frames of FIGS. 1a-1f, the reference signals are designated R0, R1, R2, and R3 and are transmitted from a first, second, third and fourth antenna of the eNodeB respectively. In an E-UTRAN system, an eNodeB may include one, two or four antennas, each of which employs a different transmission diversity scheme. As shown, the sub-frame #0 may place the reference signals within different predetermined resource elements depending upon the number of antennas employed by the eNodeB.
Further, E-UTRAN supports sub-frames with both conventional cyclical prefixes and extended cyclical prefixes. As such, FIGS. 1a-1c depict sub-frames with conventional cyclical prefixes with sub-frames having fourteen symbols. On the other hand, FIGS. 1d-1f depict sub-frames with extended cyclical prefixes with sub-frames comprising twelve symbols.
In E-UTRAN, the eNodeB does not explicitly inform the user equipment of the number of antennas and, in turn, the transmission diversity scheme. Instead, the user equipment can generally analyze the provided reference signals in an effort to determine the number of antennas and/or the transmission diversity scheme employed by the eNodeB. In general, reference signals are placed throughout a sub-frame, within the PBCH and otherwise, according to the number of transmit antennas at the base station. The reference signals are mainly intended to be used for channel estimation purposes. Regardless of a reference signal's location within the sub-frame, detecting the presence of a reference signal can allow user equipment to determine the number of transmit antennas at the base station. However, there is evidence that such a procedure is not reliable at the low signal-to-noise ratio conditions where the PBCH is designed to operate. Referring now to FIGS. 1a-1c, the PBCH is comprised of symbol #3 and symbol #4 of slot #0, and symbol #0 and symbol #1 of slot #1. In the single antenna configuration of FIG. 1a, symbol #4 of slot #0 and symbol #0 of slot #1 contain reference signals that provide antenna configuration information. Referring now to the two antenna configuration of FIG. 1b, symbol #4 of slot #0 and symbol #0 of slot #1 contain reference signals associated with the first and second antennas of the eNodeB designated R0 and R1, respectively. Similarly, referring to the four antenna configuration of FIG. 1c, symbol #4 of slot #0 and symbols #0 and #1 of slot #1 contain reference signals associated with four antennas, namely, R0, R1, R2, and R3. By analyzing the reference signals, the user equipment can attempt to determine the number of antennas and, in turn, the transmission diversity scheme employed by the eNodeB, such as space-frequency block codes (SFBC) used by two antenna eNodeBs and frequency switched transmit diversity (SFBC-FSTBC) used by four antenna eNodeBs. The user equipment can similarly analyze the PBCH or the reference signals in the sub-frames with extended cyclical prefixes of FIGS. 1d-1f in an effort to determine the antenna configuration information, except that the PBCH in the extended cyclical prefix cases is associated with symbol #3 of slot #0 and symbols #0, #1, and #2 of slot #1.
However, while antenna configuration information can be derived from the reference signals, the user equipment is, at least initially, not aware of the antenna configuration and/or the transmission diversity scheme prior to receiving and demodulating the PBCH. Further, since the antenna configuration information is needed to properly demodulate data and control channels, data loss and latency can result if the user equipment incorrectly identifies the antenna configuration and/or the transmission diversity scheme or if the user equipment is slow in identifying the antenna configuration and/or the transmission diversity scheme. As a result, some user equipment is designed to make assumptions regarding the antenna configuration and/or transmission diversity scheme. These assumptions of antenna configuration and/or transmission diversity scheme may be made prior to, or during demodulation of the PBCH and may not always be correct. In this regard, user equipment may reach an assumption regarding the antenna configuration and/or transmission diversity scheme based on a subset of the information in the PBCH. For example, in some instances, an early PBCH decoding scheme may be utilized which uses information gathered from the first of four bursts of information comprising the PBCH. Similarly, noise in the received signal may also affect the user equipment's assumption regarding an antenna configuration and/or transmission diversity scheme.
The error rate associated with the user equipment's assumption of the antenna configuration and/or the transmission diversity scheme or at least the adverse consequences which flow from an incorrect assumption can be exacerbated due to the conventional mapping of the PBCH within a sub-frame. For example, consider the PBCH of the sub-frames in FIG. 1b (for a two antenna base station) and FIG. 1c (for a four antenna base station). Note that the first three symbols of the PBCH are identical with respect to the reference signals, namely, symbols #3 and #4 of slot #0, and symbol #0 of slot #1. It is not until the final symbol of the PBCH that a difference in the antenna configuration can be ascertained as a result of the provision of R2 and R3 providing information regarding the third and fourth antennas, respectively. As such, the similarities of the PBCH for a two antenna configuration and a four antenna configuration can increase the error rate associated with the user equipment's assumption of the antenna configuration and/or the transmission diversity scheme or at least the adverse consequences which flow from an incorrect assumption.
Additionally, conventional diversity schemes for PBCH share large portions of signals. As such, an incorrect selection of a diversity scheme implemented to decode the PBCH can result in a proper decoding of the PBCH. The incorrect selection may then be used further which can result in substantial errors in communications. Under the conventional PBCH mapping this result can occur relatively frequently when considering that the various antenna configurations share a large number of resource elements.
Thus, in order to avoid or reduce the loss of data and communication latency, it would be desired to provide an improved technique for more reliably determining the antenna configuration and/or transmission diversity scheme of a network entity, such as a base station.